OSMIUM SUBCARBONYLS ON GAMMA-ALUMINA - CHARACTERIZATION OF THE METAL-SUPPORT BONDING BY INFRARED, NUCLEAR-MAGNETIC-RESONANCE, AND X-RAY-ABSORPTION SPECTROSCOPIES

[Os3(CO)12] reacted with the surface of gamma-Al2O3 to give a supporte d osmium carbonyl cluster, which was fragmented under He at 150-degree s-C to give osmium subcarbonyls. These surface species were characteri zed by infrared, C-13 NMR, and extended X-ray absorption fine structur e (EXAFS) spectroscopies and by X-ray absorption near edge spectroscop y (XANES). They are formulated as [Os(CO)x{HOAl}y{OAl}z], where the br aces represent groups at the gamma-Al2O3 surface and x is 2 or 3 and y + z = 6 - x. When the osmium tricarbonyl (x = 3) was treated under va cuum at 300-degrees-C, it lost one CO ligand and gained one surface ox ygen ligand. The surface species are both coordinatively saturated and characterized by an Os-O(support) bonding distance of 2.17 angstrom; in these respects, they are close analogues of organometallic compound s.